This invention relates to therapeutic treatment of the epidermis, and more particularly to the use of lasers for surgical and dermatological treatment.
In recent years there has been significant growth in the use of lasers to treat epidermal conditions, such as vascular and pigmented lesions, tattoo removal, depilation, and the like. A variety of laser systems have been developed for these applications, many being based on the premise that the various constituents of the epidermis have widely varying absorption characteristics of different wavelengths of light. For example, hemoglobin, a primary light absorber in blood, has a peak absorption function between 0.4 .mu.-0.5 .mu., whereas water constituents have a minimal absorption at this wavelength range. Thus laser systems for treating vascular lesions are designed to operate in this range. In contrast, water, a basic component of soft tissue, has a peak absorption characteristic at about 3 .mu.. Tattoo dyes have varying absorption characteristics, based on their color. Melanin, a primary pigment, is concentrated in pigmented lesions and hair, and has good absorption in the range of 0.3 .mu.-1.0 .mu.. A laser system operating in the 0.6 .mu.-1.0 .mu. range can treat pigmented lesions and carry out depilation while avoiding significant absorption by hemoglobin.
Thus it is clear that the wavelength of laser light is a critical factor in determining which epidermal structures are selectively affected, and which are unscathed by the treatment. Most laser systems generate only one wavelength, and are therefore limited to treating only one or a limited number of epidermal conditions. The limited usage of a laser system, which is often an expensive item, can limit its viability as a medical instrument, due to the economic realities of modern medicine.
Multi-wavelength laser system have been devised to overcome such limitations in usage. For example, tunable dye lasers can generate a wide range of wavelengths, depending on the dye being used and the configuration of the resonant cavity. However, dye lasers are extremely complex and expensive, and difficult to maintain. The dye solution must be renewed frequently, and the systems for circulating and cooling the dye solution can become maintenance and operating difficulties.
Another technique for achieving multi-wavelength operation is the use of a frequency conversion medium. For example, a KTP or LBO optical crystal can double the frequency of a laser beam, resulting in an output that has one-half the wavelength of the incident laser beam. There is a substantial loss of output power in these systems, necessitating a far larger laser system with its attendant cost and maintenance. Furthermore, these optical crystals are generally limited to frequency doubling, thereby limiting the selection of output wavelengths to a few choices based to the choices of lasing mediums.
Some dermatology treatment systems use a broadband light source to provide actinic radiation, rather than a laser light source. Such systems are expensive, they do not provide the selectivity of monochromatic light, nor the ability to be focused into a narrow and supple optical fiber for convenient delivery to the treatment site.
There is clearly a need for a multi-wavelength laser system that can accomplish a wide range of dermatology and surgical procedures and provide cost-effective treatment.